1. Field of the Invention
This invention relates to computer-aided detection (CAD) devices in medical imaging, with particular application to the use of CAD system outputs in subsequent procedures.
2. Discussion of Background
Mammography coupled with physical examination is the current standard for breast cancer screening. Although mammography is a well-studied and standardized methodology, for 10 to 30 percent of women diagnosed with breast cancer, their mammograms were interpreted as negative. Additionally, only 10 to 20 percent of patients referred for biopsy based on mammographic findings prove to have cancer. Further, estimates indicate the malignancies missed by radiologists are evident in two-thirds of the mammograms retrospectively. Missed detections may be attributed to several factors including poor image quality, improper patient positioning, inaccurate interpretation, fibroglandular tissue obscuration, subtle nature of radiographic findings, eye fatigue, or oversight.
Computer-aided detection systems are now widely used to assist in the early detection of disease. Three systems commercially available for the detection of signs of breast cancer in mammographic images are Second Look, CADx Systems, Beavercreek, OH; ImageChecker, R2 Technologies, Sunnyvale, Calif.; MammoReader, iCAD, Hudson, N.H. An additional system for detecting signs of lung cancer in chest images is RapidScan, Deus Technologies, Rockville, Md.
In practice, CAD is applied in the following fashion. A patient arrives at an imaging facility. A technologist uses imaging equipment to create medical images. These images are then input to a CAD system. The CAD system analyzes the images and provides a visual representation of the images, marking potentially suspicious regions on a paper or electronic display. Subsequently, when the radiologist is reading the images for the patient, the CAD outputs are examined to provide potentially new areas for consideration. The utility of CAD is in prompting a radiologist to consider areas not initially detected in a first reading of the images.
When a radiologist determines a suspicious region exists, further action is required. Common options include additional imaging procedures. In some cases, the suspicious area needs to be re-imaged under different positioning, compression, and magnification settings. A common element in these procedures is that a specific portion of the body needs to be identified and re-imaged. Currently, radiologists commonly indicate suspicious areas on film images by circling regions with a grease pencil. The marked films are then sent back to the technologist, who generates the requested images. Sometimes, multiple areas are marked on the film and the technologist must get clarification from the radiologist to ensure the proper area is re-imaged. In other cases, radiologists use a specialized paper form, FIG. 1, or electronic reporting system to indicate the location of the area requiring further study. An example in a mammographic application follows.
In a film-based clinic, the technologist receives a mammographic report describing the location of the area to be re-imaged and the original medical images marked with grease pencil. The current means used by radiologists to communicate with technologists have disadvantages. In mammographic reports, a radiologist describes the suspicious lesion characteristics and location to be re-imaged with words and sometimes an approximate sketch on the standardized line art breast outline, as shown in FIG. 2. An example description is “indeterminate microcalcifications in the upper outer quadrant of the right breast.” Although technologists can locate the specified area in the films most of the time, occasionally they will require further input from the radiologist or possibly even re-image the wrong area.
Disadvantages in the current reporting method are now described. When an approximate sketch is used to help specify the location of the suspicious lesion, a simple line art drawing of breast outlines may be provided on a special purpose form. The radiologist then indicates suspicious areas by marking the intended area on the outline. For paper and electronic reporting system, a simple and standard drawing of breast outlines is used for every patient. The radiologist marks locations of suspect regions to be re-imaged. The technologist interprets the radiologist's marks and refers to the original medical images to localize the proper area for the subsequent imaging procedure. When the particular patient's anatomy is not well represented by the standard line art drawing, the technologist must make a decision based personal experience to best localize the desired region.
One difficulty with marking films with a grease pencil is that in some instances, multiple areas of suspicion are marked without sufficient clarification regarding which location to re-image. The radiologist may create the additional marks during the initial reading session when a grease pencil is used to mark candidate locations during the visual search process. This problem results from using the search imagery as a reporting mechanism. That is, the radiologist searches the films and must consider many potentially suspicious areas. The grease pencil marks help the radiologist ensure that areas found throughout the visual search process are fully considered. When the technologist uses this marked imagery to guide a subsequent procedure, many of the marks made during the search are not relevant.